1. Field of the Invention
The present invention relates to a liquid electrophotographic printing apparatus, and a printing method thereof.
2. Description of the Related Art
In general, a liquid electrophotographic printing apparatus such as a laser color printer or copier uses a developer liquid mixture of toner particles and a liquid NORPAR solvent as a developing carrier. In this case, the toner comprises a pigment of a predetermined color, an organosol combining with the pigment, and the like.
FIG. 1 shows an example of a liquid electrophotographic printing apparatus. As shown in FIG. 1, a printing apparatus is comprised of a photosensitive belt 10 circulating while supported by a plurality of support rollers 11, development units 13, which correspond to the colors of yellow (Y), cyan (C), magenta (M), and black (K), for developing an electrostatic latent image formed on the photosensitive belt 10 with developer liquid and forming a toner image, a drying unit 15 having a drying roller 15a and a heating roller 15b for drying the toner image, and a transfer unit 17 for transferring the dried toner image to a recording paper sheet P.
In the liquid electrophotographic printing apparatus configured as described above, during a printing operation, after the photosensitive belt 10 is initialized by an eraser device 12 while circulating in one direction, the photosensitive belt 10 is charged by a charger 14 to a predetermined level. On the charged surface of the photosensitive belt 10, an electrostatic latent image corresponding to predetermined image data is formed by a scanning light beam emitted from each of a plurality of laser scanning units 16. The electrostatic latent image is developed by a developer liquid supplied by a development roller 13a of each of the development units 13, and then the developer liquid applied to the electrostatic latent image is squeezed by a squeeze roller 13b. The toner in the developer liquid is formed to be a film and forms a toner image, and most of the remaining NORPAR is squeezed by the squeeze roller and is removed from the photosensitive belt 10.
The drying roller 15a absorbs NORPAR remaining in the filmy toner image while rotated by frictional contact with the photosensitive belt 10. The absorbed NORPAR is heated and evaporated by the heating 15b. Then, the toner image dried to be appropriate for image transfer is transferred to a transfer roller 17a due to a difference in surface energies of the photosensitive belt 10 and the transfer roller 17a. The toner image transferred to the transfer roller 17a is finally transferred to a recording paper sheet P passing between a fuser roller 17b and the transfer roller 17a. 
In addition, when the liquid electrophotographic printing apparatus as described above performs a printing operation at an initial stage, or performs a printing operation after a predetermined time has passed since a printing operation was performed, the liquid electrophotographic printing apparatus is driven in a state in which the drying roller 15a, the transfer roller 17a, and the photosensitive belt 10 are dried.
Therefore, the drying roller in a dried state excessively absorbs NORPAR on the photosensitive belt 10 at an early stage, and, in this process, an error in which a toner image is picked by the drying roller 15a occurs. In addition, since the transfer roller 17a in a dried state tends to absorb a liquid component from the toner image transferred from the photosensitive belt 10, the transfer roller 17a instantaneously exerts a strong absorbing force against the toner image, and cannot normally transfer the toner image to a recording sheet P.
In addition, when developer liquid is supplied to the photosensitive belt 10 in a dried state for forming an image, NORPAR of newly supplied developer liquid is absorbed to the dried toner remaining on the photosensitive belt 10 when the previous printing operation is terminated, and a pigment of a toner and an organosol of newly supplied developer liquid adhere onto the dried toner. In this case, since an attraction force between the same materials greatly acts between the dried toner and the newly supplied toner, at an early stage of a printing operation, a toner image formed on the photosensitive belt is not normally transferred to the transfer roller 17a. In addition, there is a problem in which as a toner of newly supplied developer liquid repeatedly adheres to a remaining dried toner layer, and forms an accumulated layer, the photosensitive belt 10 gradually deteriorates and the usable life of the photosensitive belt 10 shortens.
To solve the above problems, it is an objective of the present invention to provide a liquid electrophotographic printing apparatus capable of keeping carrier contents of a drying roller, a transfer roller, and a photosensitive belt in a balanced state by supplying carrier the drying roller, transfer roller, and photosensitive belt before a development mode begins, and a printing method thereof.
Accordingly, to achieve the above objective, there is provided a liquid electrophotographic printing apparatus comprising a photosensitive medium on one surface of which an image is formed; a drying roller installed to detachably contact the photosensitive medium for absorbing a liquid carrier remaining on the photosensitive medium when contacting the photosensitive medium; and a transfer roller which is installed to detachably contact the photosensitive medium, to which the image formed on the photosensitive medium is operative to be transferred when the transfer roller contacts the photosensitive medium, and which transfers the image transferred from the photosensitive medium to a recording paper sheet, wherein the printing apparatus further comprises a carrier supply means for supplying a liquid carrier to the drying roller, the transfer roller, and the photosensitive medium, and is adapted so that the rollers and the photosensitive medium can be wetted by the liquid carrier before the image is formed on the photosensitive medium, and carrier absorption and discharge between the rollers and the photosensitive medium are operative to reach equilibrium states.
To achieve the above objective, there is also provided a printing method of a liquid electrophotographic printing apparatus including the steps of warming up the printing apparatus by checking various devices in the printing apparatus while a drying roller and a transfer roller are separated from a photosensitive medium; and developing an electrostatic latent image formed on the photosensitive medium with developer liquid to form an image, wherein the printing method further includes the step of supplying a liquid carrier to the rollers and the photosensitive medium so that the rollers and the photosensitive medium are wetted by the liquid carrier before the developing step.